•182 



PODOSTEMACE/E. 



[Hypogynous Exogens. 



Order CLXXXII. PODOSTEMACE/E.— Podostemads. 



Podostemeae, Mellaril and Kunth in Hutrib. N. G. et Sp. 1. 246. (1815) ; Martins Nov. G. et Sp. 1. H. 

 (1822) ; Bartl. Ord. Nat. 72. (1830) ; Bongard in Mem. de VAead. Imp. Petersb. VI. ser. III. 6y. 

 (1834) ; Endl. Gen. lxxxv. ; Meisn. Gen. p. 122. ; Griffith in Ann. Se. Nat. ser. II. 9. 183. 



Diagnosis. — Rutal Exogens, with many-seeded fruit, which is finally apocarpous, and 



apetalous very imperfect flowers. 



Herbaceous branched floating plants without stomates or spiral vessels, and with the 

 habit of Liverworts or Scale-mosses. Leaves capillary, or linear, or lacerated 

 irregularly, or minute and densely imbricated, decurrent on the stem, 

 with which they are not articulated. Flowers axillary or terminal, 

 inconspicuous, usually Q, naked, or with a very imperfect calyx, or 

 with 3 sepals bursting through an irregularly lacerated spathe. Sta- 

 mens hypogynous, varying from 1 to an indefinite number, either 

 placed all round the ovary or on one side of it, distinct or monadel- 

 phous ; anthers oblong, 2-celled, bursting longitudinally. [Pollen shaped 

 like an hour-glass, consisting of two spherules, inseparably united in 

 Podostemon. — Griffith.] Ovary 2- or 3-celled, with numerous ascending 

 anatropal ovules attached to a fleshy central placenta ; styles or stigmas 

 2 or 3, acute and sessile. Fruit slightly pedicellate, ribbed, capsular, 

 opening by 2 or 3 valves, which fall off from the dissepiment, which is 

 parallel with them. Seeds numerous, minute, containing an exalbumi- 

 nous dicotyledonous orthotropal embryo. 



Von Martius has the following remarks upon this curious Order. 

 " It is very doubtful in what part of the natural series Podostemads 

 should be arranged ; for they are connected with so many other Orders, 

 in so various and complicated a manner, that it is probable that several 

 genera, the affinities of which will be more apparent, still remain to be 

 discovered. Nothing can be more singular than the mixture of different 

 characters which they exhibit. Thus, the structure of their spathes, 

 and the want of a true calyx and corolla, approximate them to Naiads 

 (Fluviales) and Arads, while the character of their stamens and fruit 

 is very much that of Juncaginacete ; the former of these, however, 

 differ in their lower degree of organisation, and the latter in the 

 presence of a more or less perfect perianth, and in the composition of 



\ 



heir capsule. 



U 



18 



Lemna, a genus closely allied to Arads, seems to be 

 more related to them in its spathe, hypogynous stamens, 

 habit, and mode of life, but is distinguished by its less 

 highly developed few-seeded fruit. Again, Mniopsis, in 

 its ramification, in the form and position of its leaves, 

 and in its stipules, and Lacis and Podostemon in the 

 character of their spathe and the emersion of their 

 pedicels at the time of flowering, call remarkably to 

 mind the habit of Jungermannia ; so that we should 

 probably not be far from the truth, if we were to say 

 that this Order forms a transition from Naiads (Flu- 

 viales) to Juncaginacese, on the one hand touching upon 

 Arads, and being, as it were, a sort of noble analogy of 

 Liverworts among Monocotyledons." — Nov. O. et Sp. 1 . 7. 

 So far as the general appearance of Podostermads is con- 

 cerned, this account of them may be received ; but since 

 they have a dicotyledonous not monocotyledonous embryo, 

 other affinities must be looked for. Bongard first represented their time structure, and 

 more recently Mr. Griffith has described two Indian species of Podostemon, with his 

 habitual accuracy ; entirely confirming the view which I upon mere theoretical reasoning 

 formerly took of their being Exogens. — Ed. pr. p. 190. And I am still of opinion that 

 if we have among Exogens one type of structure more nearly approaching that of 



Fig. CCCXXXIII — The Q of Hydrostachys verruculosa. 1. the calyx ; 2. the same opened to show 

 the ovary ; 3. a seed ; 4. a vertical section of it. — Decaisnc. 



Fig. CCCXXXIII. 



